1. Field of the Invention
The invention is related to the field of wafer fabrication and, in particular, to measuring the resistance of a helical coil.
2. Statement of the Problem
Wafer fabrication is a procedure composed of many repeated sequential processes to produce electrical circuits, devices, components, etc. For example, wafer fabrication is typically used to build semiconductor components, such as amplifiers or transistors. Wafer fabrication is also used to build magnetic recording or magnetic memory devices, such as magnetoresistance (MR) read elements, write elements, etc. The electrical circuits, devices, components, etc, that are formed on a wafer are referred to herein as functional components.
One type of functional component formed through wafer fabrication is magnetic recording heads. Magnetic recording heads (sometimes referred to as sliders) are used to write to magnetic recording disks and to read from magnetic recording disks, such as in a hard disk drive. The magnetic recording heads include write elements that are adapted to write bits to the magnetic recording disk. Write elements typically have the structure of a write pole, a return pole, and a yoke. A coil is wrapped around the yoke, and when current is applied through the coil, a magnetic flux is induced in the yoke which is used to write to the magnetic disk.
There are two types of coils that are typically used in a write element. One type of coil is a spiral coil. A spiral coil is flat on a single plane. The spiral coil begins at an inner radius and loops outwardly to larger radii. Each loop of the spiral coil is referred to as a turn. Another type of coil is a helical coil. A helical coil has a three-dimensional structure where the loops wrap as if around the surface of a cylinder (even though the loops may not have a perfect circular shape).
In wafer fabrication, a spiral coil may be formed through photolithographic processes by defining a photoresist on a conductive layer in the desired shape of the spiral coil. A plating process is then performed to deposit conductive metal in the photoresist opening area. The photoresist is then removed, which defines the spiral coil.
Because a helical coil is not on a single plane like the spiral coil, the helical coil is formed in multiple photolithographic steps. First, a bottom coil structure is formed from conductive material. The bottom coil structure is comprised of a plurality of traces that are disconnected from one another and aligned longitudinally on a first plane. Then multiple other steps are performed to fabricate other parts of the write element, such as the yoke of the write element. In these fabrication steps, connecting structures are built up from the bottom coil structure with conductive material. The connecting structures are used to eventually connect the bottom coil structure to a top coil structure. The top coil structure is then formed from conductive material. The top coil structure is also comprised of a plurality of traces that are disconnected from one another and aligned longitudinally on a second plane. The top coil structure connects to the connecting structure in a manner to define the helical shape for the coil. An example of fabricating a helical coil is illustrated in FIGS. 1-7.
Recording head fabricators typically measure the resistance of the coils in the write elements to determine the quality of the fabrication processes used to form the coils, and to achieve a desired resistance specification. One problem with measuring the resistance of a helical coil is that there are multiple components that contribute to the resistance of the helical coil. The bottom coil structure, the connecting structures, and the top coil structure each contribute to the total resistance of the helical coil. The resistance of the connecting structures may be of particular interest. The connecting structures are built up from multiple layers of conductive material as other elements of the write element are formed. In other words, the connecting structures are built up with whatever conductive material is being used to form other layers, whether it be Cu, Au, etc. Thus, there may be a higher chance of error in forming the connecting structures than in forming the bottom coil structure and the top coil structure.
Presently, if the resistance of the helical coil is measured and is found to be higher than desired, recording head fabricators are not able to determine which of the structures are causing the high resistance. Thus, recording head fabricators are unable to adequately determine which of the fabrication processes to modify to fix the problem.